In recent years, as magnetic recording devices, such as magnetic disk drives, flexible disk drives and magnetic tape drives, have immensely expanded their ranges of utility and gained in significance, efforts have been directed toward enabling the magnetic recording media used in these drives to be prominently improved in recording density. Particularly, the increase in surface recording density has been further growing in ardency since the introduction of the Magnet-Resistive (MR) head and the Partial Response Maximum Likelihood (PRML) technique. Owing to the further introduction of the Giant-Magnet Resistive (GMR) head and the Tunneling Magneto Resistive (TMR) head in recent years, the increase is continuing at a pace of about 100% per year. These magnetic recording media are being urged to attain a still higher recording density in future and their magnetic recording layers to accomplish addition to coercive force, Signal to Noise Ratio (SNR) and resolution. Recent years have been witnessing efforts that are being continued with the object of enhancing the linear recording density and adding to the surface recording density by increasing the track density as well.
In the latest magnetic recording devices, the track density has reached 110 kTPI. As the track density is further increased, it tends to entail such problems as causing interference between the parts of data magnetically recorded in adjacent tracks and inducing the magnetization transition region in the borderline region to constitute a noise source and impair the SNR. This fact hinders the enhancement of the recording density because it immediately results in lowering the bit error rate.
For the sake of increasing the surface recording density, it is necessary that the individual recording bits on the magnetic recording medium be formed in as minute a size as possible and enabled to secure as large saturated magnetization and magnetic film thickness as permissible. As the recording bits further decrease in size, however, they tend to entail such problems as lessening the minimum volume of magnetization per bit and inducing extinction of recorded data through the magnetization reversal caused by thermal fluctuation.
Further, since the track pitch grows small, the magnetic recording device necessitates a tracking servo mechanism of extremely high accuracy and, at the same time, generally needs adoption of the method of executing the recording in a large width and executing the reproducing in a smaller width than during the recording with a view to eliminating the influence from the adjacent tracks to the fullest possible extent. Notwithstanding that this method is capable of suppressing the influence between the adjacent tracks to a minimum, it entails such problems as rendering sufficient acquisition of the output of reproduction difficult and consequently incurring difficulty in securing a sufficient SNR.
As one means to cope with the problem of thermal fluctuation and accomplish acquisition of a due SNR or a sufficient output, an attempt to enhance the track density by forming irregularities (concavities and convexities) along the tracks on the surface of the recording medium and consequently physically separating mutually the adjacent tracks is now under way. This technique will be referred to as a “discrete track method” and the magnetic recording medium that is produced by this technique will be referred to as a “discrete track medium” herein below.
As one example of the discrete track medium, a magnetic recording medium that is formed on a nonmagnetic substrate bestowed on the surface thereof with concavo-convex patterns and enabled to acquire physically separated magnetic recording track and servo signal pattern has been known (refer, for example, to JP-A 2004-164692).
This magnetic recording medium has a ferromagnetic layer formed on the surface of a substrate possessing a plurality of irregularities on the surface thereof via a soft magnetic layer and has a protective film formed on the surface of the ferromagnetic layer. This magnetic recording medium has formed in the convexed regions thereof magnetic recording regions magnetically divided from the environments.
According to this magnetic recording medium, it is held that a high-density magnetic recording medium issuing no great noise can be formed because the fact that the occurrence of magnetic walls in a soft magnetic layer can be suppressed results in preventing the influence of thermal fluctuation from readily appearing and allowing extinction of interference between the adjacent signals.
The discrete track method is known in two kinds, i.e. a method which forms a track subsequent to forming a magnetic recording medium consisting of a number of stacked thin films and a method which forms a thin-film magnetic recording medium either directly on the surface of a substrate or subsequent to forming concavo-convex patterns on a thin-film layer ready for the formation of a track (refer, for example, to JP-A 2004-178793 and JP-A 2004-178794). The former method, often called a magnetic layer processing type, is at a disadvantage in suffering the medium to be readily contaminated during the course of production and greatly complicating the process of production as well because it requires the physical processing of surfaces to be carried out subsequent to the formation of the medium. The latter method, often called an emboss processing type, though not inducing ready contamination during the course of production, is at a disadvantage in disabling stabilization of the posture and the height of floatation of the recording and reproducing head adapted to execute recording and reproducing while floating on the medium because the concavo-convex shape formed on the substrate is fated to continue existence on the film to be formed.
A method for forming regions between magnetic tracks of a discrete track medium by implanting nitrogen ions or oxygen ions into a magnetic layer formed in advance or irradiating the magnetic layer with a laser is disclosed (refer to JP-A HEI 5-205257). This prior art reference, however, has no description about the fact of installing a resist or a mask during the course of the implantation of ions. When the resist or mask is not installed, it is difficult to restrict the implantation of ions solely to the regions between the magnetic tracks.
Further, in the production of the so-called patterned medium having magnetic recording patterns disposed with a fixed regularity for each bit, the concept of forming the magnetic recording patterns by the etching with ion irradiation or by the impartation of amorphousness to the magnetic layer is disclosed (refer to Technical Report of IEICE, MR2005-55 (2006-02), pp. 21-26 (The Institute of Electronics, Information and Communication Engineers) and U.S. Pat. No. 6,331,364).
Though U.S. Pat. No. 6,331,364 reports an experiment of installing a mask on regions excepting the regions between the magnetic tracks on the magnetic layer and irradiating the magnetic layer with ions, it fails to mention Spin-On-Glass (SOG) as a mask.
As the mask directed to the ion implantation, an organic resist or a tooth hard mask that is obtained by coating the surface of a medium with a metal or an oxide layer of SiO2 and processing the coated medium with an organic resist has been being used.
The mask of this kind, however, entails a problem in the following point.
The organic resist cannot manifest a sufficient shielding effect against the impact of ions of high energy used for the ion implantation because it has an unduly small density. It is incapable of imparting sufficient resistance (etching resistance) because it is destitute of bonding and is easily scattered by collision with ions.
By contrast, the mask that is produced by the incorporation of a layer of metal or oxide possesses shielding effect and resistance of certain level against the ion implantation. It, however, incurs such extra labor hour as in specially preparing a primary mask by using an organic resist and processing the layer of metal or oxide as a mask by dry etching. The labor hour is at a disadvantage in complicating the process and degrading the yield and the cost.
This invention is directed to a magnetic recording device facing a technical difficulty in consequence of the addition to the recording density and is aimed at greatly increasing the recording density while securing the recording and reproducing property equal to or better than the conventional product, and as well decreasing to the maximum the coercive force and the residual magnetization of the regions between the magnetic recording pattern parts, thereby eliminating the blurring that occurs during the magnetic recording and eventually increasing the recording density. Particularly concerning the discrete track magnetic recording medium that results from forming a magnetic layer as a film on a substrate and subsequently forming irregularities on the magnetic layer, this invention is aimed at providing a method for the production that remarkably simplifies the process of production and decreases the risk of contamination by excluding the step of removing the magnetic layer as compared with the conventional method necessitating the step of processing the magnetic layer, using the mask of SOG having SiO as its basic skeleton, and consequently accomplishing the formation of a mask suitable for the ion implantation without increasing the number of steps and as well providing a useful magnetic recording medium exhibiting high surface smoothness and excellent property of head buoyancy.